Long spar buoy construction and mooring method

ABSTRACT

A POSITIVELY BUOYANT LONG SPAR BUOY HAVING A LENGTH OF AT LEAST ABOUT 100 FEET AND A MAXIMUM BODY DIAMETER OF ABOUT 36 INCHES, THE BODY BEING FABRICATED OF LENGTHS OF PIPE RIGIDLY CONNECTED IN END-TO-END RELATION, THE BODY INCLUDING ANTI-FLOODING MEANS ADJACENT EACH INTERPIPE CONNECTION AND BEING BALLASTED TO FLOAT UPRIGHT WITH A SELECTED MINOR PORTION OF ITS LENGTH OUT OF WATER.

Feb. 2, 1971 a. s. LOCKWOOD, JR..

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LONG SPAR BUOY CONSTRUCTION AND MOORING METHOD Original Filed May 9,1966 s Sheets-Sheet s INVENTORJ. 5mm! 5? lawn mm? United States Patent3,559,223 LONG SPAR BUOY CONSTRUCTION AND MOORIN G METHOD George S.Lockwood, Jr., and Robert K. Atwater, Los Angeles, Calif., assignors toGlobal Marine Inc., Los Angeles, Calif.

Continuation of application Ser. No. 548,566, May 9, 1966. Thisapplication July 30, 1969, Ser. No. 863,402 Int. Cl. B63b 21/26, 21/52US. Cl. 9-8 Claims ABSTRACT OF THE DISCLOSURE A positively buoyant longspar buoy having a length of at least about 100 feet and a maximum bodydiameter of about 36 inches, the body being fabricated of lengths ofpipe rigidly connected in end-to-end relation, the body includinganti-flooding means adjacent each interpipe connection and beingballasted to float upright with a selected minor portion of its lengthout of water.

This application is a continuation of application Ser. No. 548,566 filedMay 9, 1966 and now abandoned.

This invention relates to a novel marine buoy and to a method formooring the buoy for minimum loading on the buoy.

There presently exists a significant need for increased knowledge aboutthe earths oceans and about the weather over the oceans. Suchinformation is required both for military purposes and for commercialpurposes. For example, military personnel, seeking to improve oraccurately predict sonar performance, require data regarding theexistence of thermoclines. Oceanographic data is required to determinethe existence and location of profitable undersea mining areas andundersea agricultural areas, as well as to predict optimum shippingroutes. In the latter instance, optimum routing of surface vessels toavoid adverse sea-state conditions can increase the efficiency ofshipping by approximately 20%. A 20% increase in efficiency isequivalent to approximately a 100% increase in ship horsepower.

Proper instrumentation of the ocean is a major problem in acquiringreliable data regarding the ocean and its weather. Ideally, theinstrument platform or vehicle should be relatively motionless, ruggedand low in cost. The use of conventional surface buoys to carrymeasuring instruments is not satisfactory since a surface buoy respondsdirectly to wind and wave action. As a result, the sensitive instrumentsrequired for oceanographic measurements are continuously subjected toadverse dynamic loadings when mounted on surface buoys. Moreover, wherethe instrument vehicle is a surface buoy, wind and wave action causesthe buoy to move rapidly from its desired location unless the buoy ismoored in position. Movement of a surface buoy across the ocean surfacecan be avoided successfully by mooring the buoy to the ocean bottom ifthe mooring system is capable of withstanding the extreme sea conditionloads imposed upon the buoy. Complicated and costly mooring systems mustbe used with surface buoys, particularly where water depth is great.

This invention provides a novel buoy which is particularly suited foruse as a vehicle for oceanographic instrumentation. The buoy provides aninstrumentation platform which is relatively motionless even in aseverely agitated sea. The buoy is rugged and exceptionally low in cost.Moreover, such a buoy may be moored easily and satisfactorily by asimple and economic mooring system provided by this invention. The buoyhas a feature that it may provide a secure mounting platform for aplurality of instruments spaced apart from each other over ice aconsiderable distance vertically through the ocean adjacent the oceansurface.

Generally speaking, this invention provides a surface piercing buoyantmarine structure which is of a type referred to herein as a long sparbuoy. The buoy has an elongate, substantially hollow tubular body havinga length many times greater than the maximum transverse dimension of thebody. The body is comprised of a plurality of substantially identicalhollow tubular members. The buoy includes means for connecting thetubular members together in end-to-end relation. Watertight bulkheadmeans are provided transversely of the interior of each tubular memberadjacent each end thereof for preventing flooding of the member in theevent of leakage of the adjacent connecting means. Ballast means arecarried by the body adjacent one end thereof for causing the buoy tohave a center of gravity closer to the one end of the body than thecenter of volume of the portion of the body lying within a body of waterwithin which the buoy may be disposed.

Also, in combination with a long spar buoy having a low increase indisplacement per foot of increased draft, this invention provides anovel mooring system for mooring the buoy in a body water. The mooringsystem comprises an anchor for engaging the bottom of the body of waterat a desired location. A length of buoyant cable is secured at one endto the anchor. A length of non-buoyant mooring cable, having asubstantially uniform weight per foot of length, is secured at one endto the other end of the buoyant cable. The other end of the non-buoyantcable is adapted to be secured to the lower end of the buoy.

The above-mentioned and other features of the present invention are morefully set forth in the following detailed description of the invention,which description is presented with reference to the accompanyingdrawings, wherein:

FIGS. 1, 2 and 3 are views of spar buoys in accord with this invention;

FIG. 4 is an enlarged view, in partial cross-section, of a portion of aspar buoy;

FIGS. 5, 6, 7, 8, 9 and 10 are graphs setting forth various physicalcharacteristics of a family of spar buoys;

FIG. 11 is an elevation view of a spar buoy mooring system; and

FIG. 12 is an elevation view of another spar buoy mooring system.

In the following description and in the accompanying drawings, identicalnumbers are used to indicate identical or substantially identicalelements of structure in the several buoys illustrated.

-A surface piercing long spar buoy 10 is shown in FIG. 1 floatingvertically in a body of water 11 having a free surface 12. The buoy hasan elongate substantially hollow body 13 comprised of an indeterminatenumber of similar elongate tubular elements 14. The tubular elementspreferably are fabricated from sections of oil well drill pipe or wellcasing pipe; each pipe section is as long as is convenient andpracticable, say from 20 to 40 feet. The pipe lengths are essentiallyrigidly secured together in end-to-end relation by pipe coupling collars15. Preferably, the ends of the pipe lengths are welded to the collars.If desired, however, the ends of the pipe lengths may be accuratelymachined to define precision threads which are screwed into similarthreads machined on the interior of each collar. An epoxy thread-sealingcom pound is applied to the threads just before the joint is made up andcures in the assembled joint. As a result, the joints between adjacentpipe lengths are made up watertight to seal the interior of the buoy.

A platform 17 is carried by the uppermost pipe length in the body ofbuoy 10 above water surface 12 and mounts a radio antenna 18. Theantenna is coupled to a suitable transmitter (not shown) located withinthe buoy adjacent the platform for transmission of radio signals to aremote receiving station. It will be understood, however, that anydesired payload other than, or in addition to the antenna and thetransmitter may be carried by the buoy on the platform or elsewhere onor in the buoy. A suitable oceanographic instrument transducer 19 iscarried on the exterior of the buoy adjacent its lower end 20. Thetransducer is coupled to the transmitter by a signal transmissionconductor cable 21 which extends upwardly along the exterior of the buoyto a guide sleeve 22. The sleeve extends downwardly from platform 17 toan open lower end below water surface 12. The cable is secured to thebuoy at selected locations along the length of the buoy by straps orbands 23. Also, the antenna mounts additional transducers, such as awind velocimeter 24, for monitoring weather conditions over the water inwhich the buoy floats.

The spar buoys shown in FIGS. 1, 2 and 3 have lengths which are manytimes greater than their diameters. A buoy in accord with this inventionmay have a length of from about 100 to 3200* feet or more and the pipelengths from which the buoy is constructed may have a diameter of from 4to 24 inches, or even 36 inches. Where the buoy is of considerablelength, the lower sections of the body may be fabricated from strongersections of pipe than are used for the upper buoy sections. Consistentwith the hydrostatic loads imposed upon the buoy, it is desired that thebuoy be as light in weight as possible to maximize its buoyancy and tominimize the cost of the materials used in its construction. Forexample, the pipe lengths used to construct the uppermost portion of thelength of buoy :10, such as pipe lengths 25 shown in FIG. 4, may have a10.75 inch outer diameter and an inner diameter of 10.192 inches and beof H-4O grade steel. Such pipe may be used to fabricate the upperthousand feet of buoy. Below 1000 feet, however, because of the pressurewhich the water outside the buoy exerts upon the buoy tending tocollapse the pipe, stronger pipe sections must be used. Accordingly, thenext portion of the length of the buoy, down to approximately 2000 feetfrom the water surface, is fabricated of larger diameter pipe 26, orheavier wall pipe or pipe made from higher grade steel, or a combinationof these variations. Pipe lengths 26, for example, may have an outerdiameter of 13.375 inches and inner diameter of 12.615 inches and befabricated of J-55 grade steel. Below 2000 feet, the pipe used to definebuoy body 13 may have an outer diameter of, say, 13.375 inches and aninner diameter of 12.515 inches. Where the outer diameters of adjacentpipe lengths change across a connection in the length of the buoy, abell reducer connector 27 is used, as shown in FIG. 4. It will beunderstood, however, that in many cases the lower or an intermediateportion of the buoy need not be buoyant, and in instances, thenon-buoyant portions of the buoy may be made of small diameter pipe.

'In view of the usual extreme length of the long spar buoys describedherein, the buoys are subjected to considerable lateral loading in useby ocean currents and by wind and wave action upon the buoys. Since thebuoys may tend to rotate in use, these lateral loadings, particularlythe current loadings, induce the buoys to flex cyclically. such cyclicflexing may cause the joints between adjacent pipe lengths to leak.Accordingly, each tubular element, i.e., pipe length, used infabricating a long spar buoy is provided with a bulkhead plate 28adjacent each of its ends. Each bulkhead plate is disposed across theinterior of the pipe and is welded about its periphery to the walls ofthe pipe to provide a watertight seal across the interior of the pipe.If a connection between adjacent lengths of pipe should leak, the buoywill flood only to the extent of the volume defined between the bulkheadplates on opposite sides of the joint. If desired, a lifting pad 29 maybe welded to one of the 4 bulkheads on each length of pipe so that thepipe may be handled conveniently after the bulkheads have been installedand prior to interconnection of the pipe lengths.

Since it is desired that buoy 10 float with a portion of its length, say25 feet, projecting above water surface 112, and since the buoy, interms of its length, is of substantially constant external diameteralong its length, it is necessary to ballast the buoy at its lower endso that the buoy has its center of gravity located below its center ofbuoyancy. If this relationship is not maintained, the buoy becomesunstable and will not float vertically. (Buoys 33 and 40, shown in FIGS.2 and 3, respectively, must possess the same stability characteristics.)Accordingly, a selected length of the buoy at and adjacent its lower endis filled with ballast, such as water 30 shown in FIG. 1 relative tobuoy 10, or concrete 31 shown in FIG. 2 relative to buoy 33. Sand, steelshot, or other dense materials may also be used to advantage as ballast.

FIG. 2 shows an anchored spar buoy 33 fabricated in accord with theforegoing description. A mooring cable, 34 is secured to the lower endof the buoy and extends to an anchor 35 resting on the bottom 36 of bodyof water 11. A plurality of oceanographic instrument transducers 19 arecarried by the buoy at selected locations along its length and areconnected together by a cable 37. Buoy 33, however, does not include aplatform 17 for mounting a radio antenna or the like. Accordingly, cable37 is strung downwardly from the buoy to the sea bottom and extends awayfrom the buoy to a suitable instrument metering station located eitherat shore or at a suitable submerged location remote from the buoy.Transducers 19 may be identical or they may be of different types forsensing different conditions within the body of water. By way of examplerather than limitation, the transducers may be provided for sensingtemperature, sound or water velocity, electrical conductivity,radioactivity, ambient light, water turbulence, 'water pressure,magnetic fields, seismic energy or acoustic transmission vvithin thebody of water.

FIG. 2 shows another anti-flooding mechanism which is used in long spar.buoys according to this invention. The pipe lengths in the upperportion of buoy 33, as well as of buoys 10 and 40, are filled withfoamed-in-situ closed cell plastic foam material 38. The foamed materialpreferably is low density, high pressure polystyrene foam orpolyurethane foam. The foam euros to an essentially rigid state andprevents the inner volume of the pipe sections from flooding if a jointshould leak or if a leak develops in a pipe section between joints.Flooding of a single pipe section in the upper portion of a long sparbuoy could result in the buoy becoming unstable; such a result cannotoccur if a pipe section below the center of gravity of the buoy becomesflooded. Also, the foam is so light that its presence in the buoy doesnot cause an appreciable rise in the buoys center of gravity. If foamedplastic is installed within the lower portions of the buoy to checkflooding, the foam also provides a lightweight device for resistingcollapse of the buoy because of hydrostatic pressure outside the buoy.The foam material preferably is used in lieu of bulkheads 28, but it maybe used in combination with the bulkheads if desired.

In many instances, it may be desired to provide a spar buoy which cannotmove from a desired location in response to ocean currents or the like.Such a buoy normally is desired for use in relatively shallow depths ofWater, such as depths of water up to 3000- feet. FIG. 3 shows a buoy 40,in accord with the foregoing description, which has a lower extension 41disposed in a hole 42 formed in a geological formation 43 underlyingbody of water 11 and secured in place in the hole by cement 44 or thelike.

FIGS. 5-10 are graphs showing the variations in certain characteristicsof long spar buoys fabricated of 13.375 inch pipe with variations inbuoy length. FIGS. 5, 6 and 7 which show, respectively, the naturalvertical oscillatory period, the heave in various wave trains, and theangular deflection (i.e., heel or list) of long spar buoys as a functionof the length of the buoy, expressed in feet, are of particularinterest. FIG. 5 shows that as the length of the buoy increases, thenatural vertical oscillatory or heave resonance period of the buoyincreases non-linearly. It will be apparent that the input to the buoyinducing heave is directly related to the wave trains passing the buoy.The longer the wave train, the greater the period between successiveheave-inducing inputs to the buoy.

Olrve A in FIG. 6 describes the heave amplitude of a 13.375 inch outerdiameter spar buoy in a 10 foot by 12 second wave train, i.e., a wavetrain in which the troughto-peak height is 10 feet and a wave crestpasses a fixed point every '12 seconds. Curve B describes the heaveperformance of such a buoy in a 25 foot by 12 second wave train, andcurve C relates the performance of such a buoy to a 50 foot by 20 second'wave train. Curve C shows that in a 50 foot by 20 second wave train,such a buoy 600 feet long will have a heave amplitude of 4.7 feet, abuoy 1200 feet in length will have a heave amplitude of 3 inches, and abuoy 3200 feet in length will have a heave amplitude of less than of aninch. It is apparent, therefore, that a buoy according to this inventioncan be provided to have any heave characteristic desired. As a result,such buoys can be made extremely stable regardless of the severity ofthe sea-states to which they must be subjected. Such buoys are ideal foruse as vehicles or platforms for oceanographic instrumentation arrays.

As an alternative to extending the length of the buoy to reduce heaveamplitude, the cross-sectional area of the buoy at some point below thewater surface may be made a selected amount larger than the diameter ofthe buoy at the water surface. If such an expedient is to be used, it ispreferred that circular anti-heave plates, rather than elongated, extralarge cylindrical sections of buoy body, be used. Such plates functionin a manner analogous to dash pots to oppose induced heave motions.

FIG. 7 described the angular deflection (heel or list) of the upper endof a 13.375 inch diameter rigid long spar buoy relative to a verticalreference line through the lower end of the buoy in response to thecombined action of sea currents, and wind and wave forces applied to theupper end of the buoy as well as lateral components of mooring forcesapplied to the buoy; it will be understood that bending of the buoyalong its length will be superimposed upon the deflection represented byFIG. 7. The sea conditions relating to FIG. 7 are 100 knot winds, 25foot waves, and ocean currents like those found in the Thresher SearchArea. In the Thresher Search Area, ocean currents in the first thousandfeet of water below the ocean surface are substantially uniform at .9feet per second. Below 1000 feet, ocean currents are substantiallyuniform at about .4 feet per second. The angular deflection of the buoy,as well as the lateral movement of the upper end of the buoy in responseto the action of wave trains alone, is of concern where the buoy is tobe used as a supporting vehicle for an oceanographic instrumentationarray, particularly where the buoy carries an abovesurface transmissionantenna. Angular deflection and lateral movement of the upper end of thebuoy has an effect upon the effectiveness of signal transmission fromthe antenna. FIG. 7 shows that the angular deflection of the upper endof the buoy decreases with increasing buoy length.

As shown in FIG. 8, the payload capacity of a long spar buoy (consideredas a function of buoyancy before ballasting the buoy) does not increaselinearly with buoy length since heavier pipe sections must be used inthe lower portions of longer buoys to resist hydrostatic collapsepressures. The buoyancy, and thus the payload capacity of a long sparbuoy is dependent upon the submerged length of the buoy and itsdiameter. For example, a 3200 foot buoy 16.00 inches in diameter has apayload capacity of 14,500 pounds, whereas the same length buoy 13.375inches in diameter has a payload capacity of about 8000 pounds. Becauseballast usually is required to impart stability to a long spar buoy, itis preferred that concrete ballast be used since it is more dense thanwater and a smaller mass of concrete, producing a smaller offset againstpayload capacity than 'water, produces the desired gravity correctionmore effectively, in terms of buoy payload capacity, than water ballast.

The resistance of a long spar buoy to drift through the ocean inresponse to ocean currents is greater than for buoys which are locatedessentially entirely at the Water surface. For example, if a 3200 foot,13.375 inch long spar buoy were placed in the ocean in the area wherethe SSN 593 Thresher sank, it would drift only .4 mile per hour, whereasa conventional surface buoy would drift .9 mile in the same time. Thelower drift rate of a long spar buoy is attributable to the presence ofa significant portion of the length of the buoy in the lower reaches ofthe ocean where currents are not as strong as near the surface. Inmid-ocean, rather than adjacent a continent, where currents generallyare strongest, an unmoored long spar buoy would remain within arelatively small area of the ocean for several months. The researchvessel FLIP, which has a length of only 300 feet, had a mid-ocean driftof only 60 miles in 30 days.

FIG. 9 shows the effect of buoy length, again for a 13.375 inch diameterbuoy, upon drift for a buoy subjected to ocean currents like those inthe Thresher Search Area.

Because a long spar buoy has a cross-sectional area which is very smallrelative to its submerged volume, and because such a buoy has verticalwalls, it has a very low figure of increased buoyancy per increased footof draft and a very high figure of increased draft (in feet) per poundof increased load. For this reason, long spar buoys show a pronouncedincrease in draft as vertical loads on the buoy are increased. As aresult, because of their sensitivity to vertical loads, long spar buoyspresent unique mooring problems. For example, a 13.375 inch diameterbuoy will sink about one foot for every 60 pounds additional verticalload. Conventional mooring systems, which impart large vertical loads onthe moored object in proportion to the lateral constraining forceapplied to the object, cannot be used with long spar buoys such as buoy10 which carries a radio transmission antenna at its upper end.

On the other hand, long spar buoys, as shown in FIG. 10, permit the useof mooring systems which exert little force in a horizontal direction,as compared with conventional surface buoys. FIG. l0, relating to a longspar buoy 13.375 inches in diameter, shows the variation with buoylength in the force which must be applied horizontally to the buoy tokeep the buoy in a selected position in the ocean when the buoy issubjected to knot winds, 35 foot waves and ocean currents like thoseencountered in the Thresher Search Area. While such is not apparent fromthe graph of FIG. 10, a 3200 foot, 13.375 inch buoy moored in 100 knotwinds, 35 foot by 8 second waves, and Thresher Search Area currents,would experience average static horizontal mooring loads of about only1480 pounds; a conventional surface buoy of like capacity would requirea mooring system capable of withstanding an average static horizontalload of about 40,000 pounds. Vertical mooring loads for long spar buoysare essentially negligible because of the negligible heave of suchbuoys.

The curve shown in FIG. 10 was obtained by assuming that the buoy isflexible and follows, by a factor of from one-third to one-half, thehorizontal displacement of a water particle in a wave train, the actualdisplacement of a water particle varying with the average depth of theparticle below the water surface.

From the foregoing discussion of the mooring characteristics of a longspar buoy, it is apparent that conventional mooring systems cannot beused with such buoys.

7 Accordingly, this invention provides a novel mooring system and methodfor use with long spar buoys. FIG. 11 shows a mooring system 50 for along spar buoy 51 moored in body of Water 11, such as an ocean. Thesystem includes an anchor 52 which rests on the ocean fioor and isconnected to one end of a length of positively buoyant mooring cable 53.Cable 53 preferably has a uniform weight per foot. Alength ofnon-buoyant mooring cable 54, preferably having a substantially uniformweight per foot, is connected between cable 53 and the lower end of thebuoy. If the water depth over the anchor is 3000, cable 53 may beprovided by a ,000 foot length of 1 /2 inch polypropylene cable. Cable54 may be a 2000 foot length of /2 inch steel cable. Steel cable ispreferred over weighted polypropylene cable in the upper portions of themooring system because sharks have been found to have an appetite forpolypropylene. The anchor may be a 5000 pound mushroom anchor. Mooringsystem 50 has the feature that the vertical component of mooring load,this component being fully imposed upon the buoy, is small over therange of horizontal mooring load components sustained by the system.

FIG. 12 shows a presently preferred mooring system 60 for use with buoy61. The system comprises an anchor 62, a length of buoyant mooring cable63 connected to the anchor, and a length of non-buoyant mooring cable 64connected between the anchor and the buoy. The cables preferably havesubstantially uniform weights per foot of length and are substantiallyequal in length. Also, the total length of the cables is substantiallygreater than the depth of water over the anchor, although neither lengthis as long as the water is deep over the anchor. A metallic cable ispreferred for cable 64. When system 60 is subjected to a horizontal loadof 1000 pounds, the vertical load imposed upon the buoy is only 630pounds. The positive buoyancy of cable 63 should be equal to thenegative buoyancy of cable 64. The natural catenaries of the cables inthe system result in minimal increase in vertical load upon the buoy foran increase in the horizontal load imposed upon the mooring system.

Mooring system 60 has several beneficial features. When used with a longspar buoy, none of the cables of the system is in the portion of theocean closely adjacent the water surface. The mooring system, therefore,is safe from shark bite hazards. Sharks readily bite through mooringcables of surface buoys, and such action by sharks poses a seriousproblem in the mooring of surface buoys and the like. System 60 providesa spring action on buoy 61 which acts to return the buoy to over theanchor after the buoy has been moved laterally by a storm or the like.The non-buoyant cable keeps the buoyant cable from the water surface,and the buoyancy of cable 63 prevents bottom fouling of this cable. Allthese features are provided in a mooring system which effectivelyrestricts movement of the buoy from a desired location in the ocean.

Both mooring systems described benefit from the low heavecharacteristics of long spar buoys. Because the buoys do not heaveappreciably, the loading upon the associated mooring system isessentially constant and any cyclic loads are of low magnitude relativeto the average static loading of the system. As a result, the componentsof the mooring systems do not fatigue.

The invention has been described above by reference to certainstructural arrangements which have been presented merely by way ofexample in furtherance of a complete and comprehensive explanation ofthe invention. It will be realized that these examples do not encompassall forms which the invention may take, and that the structuresdescribed may be altered or modified without departing from the scope ofthe invention. Ac-

cordingly, the foregoing description is not to be regarded as limitingthe scope of the invention.

What is claimed is:

1. A long spar buoy comprising an elongate substantially hollow andpositively buoyant body having a length many times greater than themaximum transverse dimension thereof, the body being comprised of aplurality of substantially identical tubular members having a maximumdiameter of about thirty-six inches, the body having a length greaterthan about one hundred feet, means connecting the members together inend-to-end relation, watertight bulkhead means transversely ofthe'interior of each member adjacent each end thereof for preventingflooding of the member in the event of leakage of the adjacentconnecting means, and ballast means carried by the body adjacent one endthereof for causing the bow to have a center of gravity closer to theone end thereof than the center of volume of the portion of the buoylying within a body of Water in which the buoy may be disposed.

2. A long spar buoy according to claim 1 wherein said tubular membersare lengths of pipe and all of the lengths of pipe in said pluralityhave an outer diameter in the range of from about four inches to aboutthirty-six inches.

3. In combination with a long spar buoy adapted to float vertically in abody of water with its upper end disposed above the surface of the waterand having substantially no vertical heave in response to passing wavesand a low factor of increase in displacement per foot of increaseddraft, a buoy mooring structure comprising an anchor for engaging thebottom of the body of water at a selected location on the bottom, alength of buoyant mooring cable secured at one end thereof to theanchor, and a length of non-buoyant mooring cable of substantiallyuniform weight per foot of length secured at one end to the other end ofthe buoyant cable and secured at its other end to the lower end of thebuoy, the buoyant and non-buoyant cables being substantially equal inlength and having a combined length which is substantially greater thanthe depth of water over said location.

4. The combination of claim 3 wherein the positive buoyancy of thebuoyant cable is substantially equal to the negative buoyancy of thenon-buoyant cable.

5. In combination with a long spar buoy having sufficient length andsufficiently high ratio of length-to-diameter that the buoy floatsvertically in a body of water with its upper end disposed above thesurface of the water, the buoy manifests substantially no verticalmotion in response to waves moving past the buoy across the watersurface, and the buoy has a low factor of increase in displacement perfoot of increased draft, a buoy mooring structure consisting of ananchor for engaging the bottom of the body of water at a selectedlocation on the bottom, a length of buoyant mooring cable secured at oneend thereof to the anchor, and a length of nonbuoyant mooring cable ofsubstantially uniform weight per foot of length secured at one end tothe other end of the buoyant cable and secured at its other end to thelower end of the buoy, the buoyant and non-buoyant cables beingsubstantially equal in length and having a combined length which issubstantially greater than the depth of water over said location.

References Cited UNITED STATES PATENTS 2/1866 Bowlsby. 1/1967 Bossa.

